All those hours you spend killing aliens on your TV might cost you big time. If your social life hasn’t already suffered from playing video games all night long, consider this: A 20-year-old British man recently died after sitting around and playing his Xbox 360 all night without a break.

The cause? Deep-vein thrombosis, a blood clot in the lower limbs caused by prolonged sitting that can come loose and work its way up to the heart or lungs, triggering a heart attack.

As many as 2 million Americans are diagnosed with DVT annually, but thousands of cases go unreported, especially among younger desk jockeys and marathon gamers. “Since the pain is similar to a cramp, men write it off,” says John Laird, medical director of the vascular center at the University of California at Davis.

We’ll never tell you to lay off the video games entirely but it’s important to take regular breaks from the action. Pause your game every hour and walk around for a few minutes to keep your blood flowing, says Ryan Venis, M.D., co-vice director of emergency medicine at St. Vincent Hospital, Indianapolis.

And don’t forget to drink plenty of water: Keeping hydrated (250ml every 2 hours) during long sitting spells ensures healthy bloodflow and prevents clotting, Laird says.